Researcher has learned how to maximize the cancer-fighting power of broccoli

May 15 2004

University of Illinois researcher Elizabeth Jeffery has learned how to maximize the cancer-fighting power of broccoli. It involves heating broccoli just enough to eliminate a sulfur-grabbing protein, but not enough to stop the plant from releasing an important cancer-fighting compound called sulforaphane.

The discovery of this sulfur-grabbing protein in the Jeffery lab makes it possible to maximize the amount of the anticarcinogen sulforaphane in broccoli.

Jeffery's research will be published in an upcoming issue of Phytochemistry. She is a professor in the Department of Food Science and Human Nutrition at the U of I.

"As scientists, we learned that sulforaphane is maximized when broccoli has been heated 10 minutes at 140 degrees Fahrenheit," said Jeffery. "For the consumer, who cannot readily hold the temperature as low as 140 degrees, that means the best way to prepare broccoli is to steam it lightly about 3 or 4 minutes--until the broccoli is tough-tender."

Frozen-food manufacturers may use this technology to increase the health benefits of the broccoli they sell, allowing the consumer to heat it without having to worry about the conditions.

Jeffery said that sulforaphane is one of the most powerful anticarcinogens found in food. "It works by increasing the enzymes in your liver that destroy the cancer-inducing chemicals you ingest in food or encounter in the environment."

But the chemistry for triggering the release of sulforaphane is tricky. Sulforaphane is linked to a sugar molecule through a sulfur bond. When the broccoli enzyme breaks off the sugar to release the sulforaphane, a sulfur-grabbing protein can remove the newly exposed sulfur on the sulforaphane and inactivate it.

"Although our gut bacteria may be able to release some of the sulforaphane, we don't have the enzyme to release sulforaphane in our body tissues, so our best bet is to use the enzyme in the broccoli," Jeffery said. "The enzyme in the broccoli does a really good job of breaking that bond. You can break it simply by chopping the broccoli."

Jeffery's team of researchers began by cooking broccoli for different lengths of times at different temperatures to learn the point at which the broccoli enzyme that releases sulforaphane is destroyed.

"And, much to our excitement, after we had heated it for just a little while, we found we had killed off a protein that nobody knew was there. This protein, named the epithiospecifier protein, had been grabbing sulfur and greatly depleting the amount of sulforaphane in a serving of broccoli.

"The protein was very heat-sensitive, and with a little bit of heat, we killed it off and got an almost perfect yield of sulforaphane, the cancer-fighting component," she said.

"It was a serendipitous discovery, and it changed our focus. Instead of worrying about overcooking the broccoli and losing the enzyme that releases the sulforaphane, we focused on heating the broccoli just enough to destroy the sulfur-grabbing protein, but not enough to harm the enzyme that releases sulforaphane from the sugar," said Jeffery.

Other researchers at the University of Illinois who contributed to the study were Nathan Matusheski and Qinyan Qiao.

The study was funded by the United States Department of Agriculture. http://www.uiuc.edu